/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.core.support;

import java.util.Properties;
import javax.sql.DataSource;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.PropertiesBeanDefinitionReader;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Bean definition reader that reads values from a database table,
 * based on a given SQL statement.
 *
 * <p>Expects columns for bean name, property name and value as String.
 * Formats for each are identical to the properties format recognized
 * by PropertiesBeanDefinitionReader.
 *
 * <p><b>NOTE:</b> This is mainly intended as an example for a custom
 * JDBC-based bean definition reader. It does not aim to offer
 * comprehensive functionality.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #loadBeanDefinitions
 * @see org.springframework.beans.factory.support.PropertiesBeanDefinitionReader
 */
public class JdbcBeanDefinitionReader {

    private final PropertiesBeanDefinitionReader propReader;

    @Nullable
    private JdbcTemplate jdbcTemplate;


    /**
     * Create a new JdbcBeanDefinitionReader for the given bean factory,
     * using a default PropertiesBeanDefinitionReader underneath.
     * <p>DataSource or JdbcTemplate still need to be set.
     *
     * @see #setDataSource
     * @see #setJdbcTemplate
     */
    public JdbcBeanDefinitionReader(BeanDefinitionRegistry beanFactory) {
        this.propReader = new PropertiesBeanDefinitionReader(beanFactory);
    }

    /**
     * Create a new JdbcBeanDefinitionReader that delegates to the
     * given PropertiesBeanDefinitionReader underneath.
     * <p>DataSource or JdbcTemplate still need to be set.
     *
     * @see #setDataSource
     * @see #setJdbcTemplate
     */
    public JdbcBeanDefinitionReader(PropertiesBeanDefinitionReader beanDefinitionReader) {
        Assert.notNull(beanDefinitionReader, "Bean definition reader must not be null");
        this.propReader = beanDefinitionReader;
    }


    /**
     * Set the DataSource to use to obtain database connections.
     * Will implicitly create a new JdbcTemplate with the given DataSource.
     */
    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    /**
     * Set the JdbcTemplate to be used by this bean factory.
     * Contains settings for DataSource, SQLExceptionTranslator, etc.
     */
    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
        Assert.notNull(jdbcTemplate, "JdbcTemplate must not be null");
        this.jdbcTemplate = jdbcTemplate;
    }


    /**
     * Load bean definitions from the database via the given SQL string.
     *
     * @param sql SQL query to use for loading bean definitions.
     *            The first three columns must be bean name, property name and value.
     *            Any join and any other columns are permitted: e.g.
     *            {@code SELECT BEAN_NAME, PROPERTY, VALUE FROM CONFIG WHERE CONFIG.APP_ID = 1}
     *            It's also possible to perform a join. Column names are not significant --
     *            only the ordering of these first three columns.
     */
    public void loadBeanDefinitions(String sql) {
        Assert.notNull(this.jdbcTemplate, "Not fully configured - specify DataSource or JdbcTemplate");
        final Properties props = new Properties();
        this.jdbcTemplate.query(sql, rs -> {
            String beanName = rs.getString(1);
            String property = rs.getString(2);
            String value = rs.getString(3);
            // Make a properties entry by combining bean name and property.
            props.setProperty(beanName + '.' + property, value);
        });
        this.propReader.registerBeanDefinitions(props);
    }

}
